As conventional techniques, in JP-A-8-300352, a thermoplastic resin having a thermosetting resin coating film is mixed with a primary or secondary amine as a coating film-decomposing agent by use of an extruder to reproduce a thermoplastic resin under the conditions of a temperature of 200-300° C. and a pressure of 10-100 kg/cm2.
Furthermore, JP-A-2001-253967 discloses a process which comprises supplying a crosslinked polyethylene and water to an extruder and extruding them under the conditions making water supercritical or subcritical in the extruder, that is, at a temperature of 200-1000° C. and a pressure of 2-100 MPa to produce a thermoplastic material.
JP-A-2002-249618 discloses that a crosslinked polymer is extruded from an extruder and is introduced into a reactor together with a fluid of high temperature and high pressure to produce a reaction product, which is introduced into a separator to separate the reaction product and the high temperature fluid, and the reaction product is exhausted to the outside by use of an extruder.
JP-A-2000-198877 discloses that a thermosetting resin is reacted with a decomposing liquid in an extruder and, after the reaction, the decomposing liquid and a solid insoluble in the decomposing liquid are treated with a centrifuge in a solid-liquid-separating tank.